This invention relates to an automatic gain control and, more particularly, to an automatic gain control circuit capable of functioning with aperiodic input signals.
There are many applications such as radar, sonar and ultrasonic flow measurement, to name a few, which transmit bursts of energy, electromagnetic, ultrasonic or otherwise, at both periodic and aperiodic rates. In these applications either the transmission line of the burst of energy across a known distance is measured or the time for the burst of energy to be propagated outwardly, strike an object, and be reflected back therefrom, is measured. Regardless of the application or environment, in each case, the transmitted energy is received by an appropriate antenna, transducer, or the like, and thereby converted into electrical signals for processing. As part of the processing, these electrical signals desirably should have a constant amplitude. Otherwise, particularly where precise measurements are required, phase and other distortions can occur in the processing and measuring circuitry which create undesired errors in the measurements.
Automatic gain control is used to maintain a constant amplitude of the received signals. Among many of the known automatic gain control circuits, there is a continuously transmitted signal often having a carrier wave whose amplitude may be monitored and used to automatically control the gain of an amplifier and thereby maintain a constant received signal amplitude for the processing. In instances where the signals are aperiodic or where there is a large amount of noise present in the received signals, particularly where the said received signals are in the form of aperiodic bursts of energy, it is relatively difficult to obtain a stable reference point which may be used to monitor the received signal amplitude and thereby control and maintain constant the received signal amplitude.
Accordingly, it is an object of this invention, to obviate any of the disadvantages of the pulse type automatic gain control circuits.
A further object of this invention is to provide an improved automatic gain control circuit having particular application with aperiodic input pulses.